In foundries, molten metal is poured into a metal shaping cavity in which, upon cooling, the metal assumes the shape of the cavity as defined by surfaces at the walls of the cavity as well as by surfaces of projects extending into or suspended within the cavity. The wall surfaces and inside surfaces are typically the surfaces of bound sand elements. The outside elements are referred to as "molds," and the inside surfaces are the surfaces of elements called "cores." Of course both of these surfaces are "molding" or metal shaping surfaces. Both of these types of metal shaping elements are, in turn, formed by other "molding," i.e. sand shaping elements which, in the trade, are called "patterns," and "core boxes" respectively. Even though the "core box" term is used, the core box is, of course, a pattern, or sand shaping element, as well. Thus, in this application when the term "pattern" is used it is intended to refer to both the element for shaping the sand molds as well as to the element for shaping the sand cores.
The pattern elements, namely patterns and core boxes, are manufactured from iron, steel, aluminum, polyurethane, epoxy, and other metals and/or plastics and wood. When molds or cores are made for applications in which the sand is blown into the core box or pattern, the patterns and core boxes are provided with essential vents, and other elements. These vent elements in the patterns and core boxes are normally made from brass, plastic, etc., and often include fine mesh screens made from brass, steel, etc. Such auxiliary vent elements are not usually present in applications in which the sand is hand packed into the pattern or core box.
The pattern materials i.e. the mold-shaping and core-shaping surfaces, which benefit from the process of the present invention are any of the metallic or plastic materials referred to above, and in fact, any plastic or metallic shaping surface.
In the following examples, however, aluminum, steel, core boxes (top steel, bottom aluminum) polyurethane, epoxy, and iron patterns are provided as exemplary.
In general, problems associated with mold release in the manufacture of products may be typified by those experienced in the manufacture of particle boards, and in the manufacture of foundry cores and molds. Generally speaking poor mold release shows up in irregular surfaces in the finished product, which gets worse with successive product regardless of whether glass bottles or rubber balls are being manufactured.
In the particle board industry, four resins, phenolformaldehyde, melamine-formaldehyde, isocyanate and ureaformaldehyde resins, have been most commonly used for commercially produced interior and exterior particle boards. Of these resins, phenol-formaldehyde resins have become the standard by which all resins are measured, chiefly because they are relatively inexpensive, and have sufficient hydrolytic resistance for exterior applications. However, even phenolic resins have somewhat of a tendency to experience mold-release problems. Organic polyisocyanates have been recognized for some time as useful competitive alternate binders in the manufacture of particle boards. As known in the art and as practiced with phenol-formaldehyde resin, the isocyanate binders, whether in solution or emulsified, are mixed with the wood chip particles utilized as the base for the particle board. A wood chip and binder mixture is then formed into a mat and hot-molded in the desired size. A principal disadvantage of the use of isocyanate has been the increased tendency of the molded particle board to adhere to the cauls of the press thereby creating a buildup of wood particles on the caul, which causes succeeding particle board surfaces to be unnecessarily rough. Such a poor release of the cured particle board from the mold or caul surface creates difficulty in the automatic handling of the cauls.
Previously, the above drawbacks to the use of organic polyisocyanates as particle board binders were minimized or lessened by the incorporation of certain organophosphorus compounds, their derivatives and mixtures thereof as internal release agents with the organic polyisocyanate, as taught in the U.S. Pat. Nos. 4,257,995 and 4,024,088. However, when the organic polyisocyanate binders are mixed with phosphate compounds such as is taught in U.S. Pat. No. 4,257,995 it has been found the isocyanate mixture suffers from a short shelf life and thus must be used within a short period of time in order to avoid the formation of a hard skin or barrier on the upper surface of the isocyanate mixtures. Because of the existence of this barrier, the shelf life of the resulting isocyanate mixture becomes relatively short, thereby limiting the usefulness and effectiveness of an organic polyisocyanate binder incorporating such phosphate internal release agents.
Other approaches to this problem of adhesion of the board to the heated platens involve a sheet, impermeable to the binder resin, placed between the surface of the board and the platen during the forming process, or the coating of the surface of the platen, prior to each molding operation, with an appropriate release agent, or to coat the surface of the particles themselves with a material which will not adhere to the platen. Any of these alternatives, particularly where the process is being operated on a continuous basis, is cumbersome and a drawback to what is otherwise a very satisfactory method of making a particle board with highly attractive structural strength properties.
The problem of mold release, as stated above, is more universal than merely with respect to particle board manufacture. In a general sense then, release of molded articles from molds in which they have been formed has been achieved by coating the surface of the mold cavity with an agent which facilitates release of the molded article from the walls of the mold cavity. This procedure has severe drawbacks. The agent, after molding, adheres either to the walls of the mold cavity or to the surface of the molded article or, in the usual case, to both. Previously, after multiple moldings and application of release agent, the agent tends to build up on the surface of the mold cavity walls and eventually covers and obscures details of the mold cavity surfaces to be imparted to the molded article. Also, the presence of excessive quantities of release agent adhering to the surface of the molded article can,, impede subsequently subjecting the article to further treatment, such as painting or adhering operations. While it is possible to clean the surfaces of molded articles in preparation for painting or adhering operations, this adds to the time and expense of production. Additionally, the need to reapply the release agent after each molding or a limited number of moldings interrupts the molding operation and slows down output.